Process for preparing alloys of calcium with aluminum



Patented Feb. 13, 1940 PROCESS roe cALcr M wrrn ar. g

' Gustaf Newton Kirsebom, Westbury-on-Trym, .1 Bristol, England, assignor to'Calloy Limited, London, England, a joint-stock company of England a. Application Februar 9, 1938,

Serial No. 189,592. 11, 1937 1 Claim.

In the specification of my prior United States Patent No. 1,935,245 a process is described for the preparation of aluminum alloys including I alkaline earth metal alloys, 9. specific applica- 5 tion of which process comprises heating an alkaline earth metal oxide or carbonate in a molten bath of aluminum below the surface thereof; for example, by placing on the top of a bath of molten aluminum, pieces of alkaline earth metal oxide or carbonate of suflicient size'to overcome the surface tension of molten aluminum and sink below the surface.

In describing the carrying out of the said process of my prior patent, a temperature range was given as between 700 and 1500 C., and when working the process in order to obtain the residues in the form of unfused dross, a range of from 1000 to 1200 C. was given, and when working, within this last-named ranged of from 1000-1200 C., in the case of the preparation of calcium aluminum alloys from lime, the calcium oxide was reduced to metallic calcium which alloyed with the excess aluminum, and the alu-' line earth metal oxides or carbonates or similar I oxygen-containing compounds are heated in a bath of molten aluminum below the surface of the latter at such a high temperature (as hereinafter indicated) that, while an alloy of aluminum and alkaline earth metal is formed, the residue of the mass is fused and converted into the form of a molten slag which latter constitutes a separate layer beneath the molten alloy of aluminum and alkaline earth metal.

The temperature to which the aluminum and alkaline earth metal compound must be heated in order to obtain the formation 01' a molten slag depends upon the alkaline earth metal compound used. Thus, calcium aluminate,

CaQAlzOa formed when a calcium compound is used has a and 1600- C., may be employed, for example,

melting point about 1350 C.; and in the case of In Great Britain February 1550 0.; and if the slag material present is one.

which would not be freely molten" within this temperature range, calcium aluminate can be added thereto as a iluxing agent or there may be used as stlrting material, an alkaline earth metal compound containing lime, (for example. dolo-,

mite) but in this case, calcium will also be introduced into the magnesium or other alkaline earth metal.

The present invention will now be described with reference to the preparation of specific alkaline earth-aluminum. alloys.

In the case of calcium aluminum alloys, lime may conveniently be introduced on to the top of the bath of molten aluminum, heated (in any suitable furnace) tmmtemperature near to, but

below the boiling point of aluminum, advantageously a temperature of 1500-l600 0.; the lime being in the form of pieces of. suiilcient size to overcome the surface tension of molten aluminum (for example, pieces ranging in size from 1 mm. to 100 mm.). Under these circumstances. the following reaction takes place:

,as a batch" process in any suitable electric or other furnace.

The following is an example of the procedure which may be adopted in preparing a calciumaluminum alloy in accordance with the invention when working as a batch" process:

lbs. aluminum and 50 lbs. of lime, the latter in pieces e. g. ranging from a few mm. diameter to walnut size, are heated together in an electric arc furnace to a. temperature of 1500-1600 C., for example, 1550", i. e. near to,

but below, the boiling point of aluminum. The pieces of lime sink into the molten aluminum and reduction takes place with the formation of metallic calcium which alloys with the excess aluminum. There is thus obtained to 76 lbs. of a calcium-aluminum alloy containing 20-25% of calcium and about 45 lbs. of calcium aluminate slag. In thus working as a batch" process, at the before-mentioned. temperatures,the re- 5 duction will be completed in about three quarters of an hour.

The process may be carried out continuously by tapping ofi some of the aluminum alloy from the upper partof the furnace and some of the calcium aluininate slag from or near the bottom of the furnace, and af'urther charge added Without interruption of the process.

Apart from the advantage of obtaining a clean separation of the metal alloy from the slag, the slag produced in this case is a marketable productancl can (in an inexpensive manner, e; g. by

grinding) be used for the preparation of cements 

